When the Sun Attacks

Media outlets like IEEE Spectrum are constantly bombarded with press releases, advisories, PR pitches. Some of them we find interesting, others not so much. On Monday, my colleague Tekla Perry received an e-mail alert from the National Oceanic and Atmospheric Administration that got her attention: “Strong solar storm reaching Earth,” the subject line read, and it went on to warn that a “significant explosion from the sun’s corona Saturday morning” would likely trigger a “strong, G3 geomagnetic storm on Earth.”

Tekla wondered what was up. “I’ve been on the NOAA list for a while and never noticed this kind of warning before,” she told me.

I was curious, too, so I called up NOAA’s Space Weather Prediction Center in Boulder, Colorado, which issued the advisory. This particular storm, it turns out, was pretty garden variety. NOAA measures solar storm severity on a “G-scale” of 1 to 5, 5 being the most severe. In this case, most of the billions of charged particles streaming out from the sun blew right past our planet, so the storm only merited a G-1 or G-2 in most places. We can expect to see about 600 G-2 events in the current solar cycle, NOAA space scientist Joe Kunches told me.

So why the dire-sounding alert? It turns out that SWPC (pronounced SWIP-see) is starting a new campaign to educate the public on the existence and potentially serious consequences of solar storms. A worthy cause: Intense solar activity can trigger geomagnetic disruptions that knock out electrical grids (PDF) and damage radio and satellite telecommunications. On the plus side, solar storms also lead to gorgeous high-altitude light displays in the night sky; the photo was captured on September 27 by an amateur photographer in Yellowknife, Northwest Territories, Canada.

“Space weather is a difficult topic for the public to comprehend,” Kunches says. Apart from those vivid auroral displays, “there’s no visceral component—you can’t look out the window and know if it is or it isn’t happening.” Sending out alerts, he says, “is a way to make it less spooky to people, to let them know, hey, we’re watching the situation, we’ll keep you advised.” Along those lines, SWPC also recently set up a Facebook page.

But for those who have to deal with the consequences of solar storms—particularly power grid operators—the G-scale isn’t terribly helpful, Kunches acknowledges. It’s based on a 79-year-old metric known as the K-index, which reflects the change in the Earth’s magnetic field over a 3-hour period as measured at a site near Boulder. For instance, a K-index of 6 (which corresponds to a G-scale rating of 2) means the magnetic field fluctuated by 120 to 200 nanoTeslas over three hours. The most severe storm, a K-9, is anything over 500 nT. For comparison, Earth’s magnetic field varies from around 20,000 nT near the equator to 80,000 nT near the poles.

So here’s the problem: For the power grid, the kinds of magnetic spikes of greatest concern happen over very short intervals, of maybe just a few seconds or minutes. Those spikes, if intense enough, can trigger geomagnetically induced currents, or GICs, which in turn can damage transformers and other electrical equipment. “The K-index doesn’t tell you whether that change occurred rapidly over 1 minute or gradually over the 3-hour window,” explains John Kappenman, a power engineer who’s an expert on the impacts of solar storms on the grid. “The rate of change is what’s important for GICs—the higher the rate of change, the higher the effect.”

What’s more, the K-index tops out at 500 nT, whereas the worst geomagnetic storms are much higher. Kappenman, looking at historical records, has estimated that the May 1921 storm, considered one of the worst of the past century, resulted in disturbances of up to 5000 nT/minute. “The K-index is quite inadequate for the concerns that the power industry could have,” he says.

Kunches agrees. “The K-index is in many ways outdated and archaic,” he says. “Maybe the best thing to do is throw it in the trash can and just get the data.” With the Internet, he says, “there’s no reason that you couldn’t read out a chain of magnetometers at a high cadence and have a computer pay attention to how rapidly they’re changing.” The Electric Power Research Institute and some power companies have been experimenting with such a setup, placing magnetometers near key points in the grid. The trick, he says, is to isolate the data so you’re looking at the actual magnetic field rather than what’s coming off the wire nearby.

That still isn't the complete picture, though. What’s still lacking, Kappenman and Kunches say, is a good way of predicting which solar storms will cause trouble and which will not. Space weather scientists are constantly working to improve their forecasts. Next week, for example, SWPC will officially unveil a new model, called WSA-Enlil, that should sharpen their predictions of the onsets of solar storms. This animation shows WSA-Enlil’s forecast on September 24 of the likely path of the coronal mass ejection; the yellow dot is the sun, the green dot is Earth.

And just because this week’s storm did no real harm does not mean we’re out of the woods, Kappenman adds. The sun is waking up from a relatively quiet phase, and we can expect to see an uptick in both the number of storms and their severity in coming years. Given our thorough reliance on electricity and electronics, he believes we should be doing much more to prepare for a planet-wide super solar storm that could knock out power grids everywhere and take months if not years to recover from.

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